Question

如果在switch语句中匹配大小写，我需要发出break while循环。案例如下：如果用户输入的数字小于零或大于五。除了我提到的两个例外，我的开关工作大部分都是我的。这是我的代码：

import java.util.Scanner;
public class Product
{
    public static void main(String args[])
    {
        int cntr = 0;
        int product = 0;
        int units = 0;
        double totalcost = 0;
        Scanner MK = new Scanner(System.in);
        cntr=0;
        while (cntr >= 0 && cntr <=5)
        {
            System.out.println("Enter Product no.(1-5) or -1 to Quit");
            product = MK.nextInt();
            switch(product) {

            case 1:
            {
                System.out.println("Product " + (cntr+1));
                System.out.println("Enter Quantity or -1 to Quit");
                product = MK.nextInt();
                double cost = 2.98;
                totalcost = totalcost + cost*product;
                System.out.println("Current total cost: " + totalcost);
                cntr++;
            }
            break;
            case 2:
            {
                System.out.println("Product " + (cntr+1));
                System.out.println("Enter Quantity or -1 to Quit");
                product = MK.nextInt();
                double cost = 4.50;
                totalcost = totalcost + cost*product;
                System.out.println("Current total cost: " + totalcost);
                cntr++;
            }
            break;
            case 3:
            {
                System.out.println("Product " + (cntr+1));
                System.out.println("Enter Quantity or -1 to Quit");
                product = MK.nextInt();
                double cost = 9.98;
                totalcost = totalcost + cost*product;
                System.out.println("Current total cost: " + totalcost);
                cntr++;
            }
            break;
            case 4:
            {
                System.out.println("Product " + (cntr+1));
                System.out.println("Enter Quantity or -1 to Quit");
                product = MK.nextInt();
                double cost = 4.49;
                totalcost = totalcost + cost*product;
                System.out.println("Current total cost: " + totalcost);
                cntr++;
            }
            break;
            case 5:
            {
                System.out.println("Product " + (cntr+1));
                System.out.println("Enter Quantity or -1 to Quit");
                product = MK.nextInt();
                double cost = 6.87;
                totalcost = totalcost + (cost*product);
                System.out.println("Current total cost: " + totalcost);
                cntr++;
            }
            case 6:
            {
                System.out.println("Product " + (cntr+1));
                System.out.println("Enter Quantity or -1 to Quit");
                //product = MK.nextInt();
                //double cost = 2.98;
                //totalcost = totalcost + cost*product;
                System.out.println("Current total cost: " + totalcost);
                //cntr++;
            }
            break;
            }
            System.out.println("Total cost-->" +totalcost);
        }
    }
}

如果任何人可以指出如何在输入小于零或大于5的程序时停止我的程序，我会非常感激。

Answer 1

有两种选择：

使用您希望循环结束时设置的标记（在default或-1子句中）或
在default（或-1）条款中使用labelled statement和定向 break
在特定的情况下，您说您希望整个程序结束，您可以使用System.exit

以下是关于选项2的更多信息：

label: while (...) {          // <== Labelled statement
    switch (...) {
        case ...:
            // ...
            break;            // <=== Normal (undirected) break, just exits what
                              //      it's in (switch in this case)
        // ...
        default:
            break label;      // <=== Directed break, exits loop
    }
}

它对于嵌套循环也很方便。

旁注：您{条款中的陈述不需要}和case。 case的代码一直持续到break。（是的，它与其他陈述有点不同。）

附注2：您在提示中说过Enter Product no.(1-5) or -1 to Quit，但您有1到 6 （含）的值。你可能意味着Enter Product no.(1-**6**) or -1 to Quit。

在Java中逐个循环打破

1 个答案: